Antimony oxide glass



Dec. 221, 1959 Filed May 18, 1955 B. W. KING. JR., ETAL ANTIMONY OXIDE GLASS 20 40 e0 e0 Mm /sb203 R20 0.50 x20 0.50 N020) 2 Sheets-Skaai. 1

Mol S0203 Mol cvc, S0203 1N V EN TOR.

Burnham W. King Wolter A. Hedden ATTORNEYS.

Dec. 22, 1959 B. w. KING.'JR., ET AL 2,918,382

ANTIMONY oxIDE GLASS Filed May 18, 1955 2 sheets-sheer 2 Fig f "/o Transmission I 2 3 4 5 6 Wavelength, microns INVENTOR. Burnham W. King A. dden BY, Wolter He A 7 TORNE YS.

United States Patent "ce 2,918,382 ANTIMONY oXIDE GLASS Burnham W. King, Jr., Columbus, and Walter A. Hedden, Worthington, Ohio, assignors, by mesne assignments, to Bradley Mining Company, San Francisco, Calif., a corporation of California Application May 1s, 195s, seria1N0.so9,1s1 s claims. (ci. 10s- 47) This invention relates to glass compositio'ns having an oxide of antimony as the primary constituent.

Silica and silicate glasses are comparatively inexpensive to manufacture and have satisfactory light-transmission characteristics in the visible range. These glasses are substantially opaqueto infrared rays longer than about 3.5 microns, and so are not suited fo'r uses where transmission of infrared rays beyond this wave length is required.

Glass compositions having arsenic trisulde as the predominant constituent have been developed for use especially where infrared transmission is required. These glasses are relatively expensive to manufacture and present dangers to workmen engaged in their manufacture by reason of the toxicity of the arsenic, although they have good infrared transmission.

It is an object ofthe present invention to form a glass which has good infrared transmission characteristics and at the same timedis relatively economical to manufacture and less toxic to workmen than glasses co'ntaining arsenic compounds.

A further object of the present invention is to form a glass with antimony oxide as the predominant constituent and substantially free of silica and boron trioxide.

These and other objects will appear in the disclosure which follows.

According to the present invention there is provided a novel transparent glass composition which transmits infrared radiation of wave lengths up to about 6 microns, having antimony oxide as its principal constituent and also' containing alumina and either potassium oxide, so-

diurn oxide, or both. No other ingredients are ordinarily` present except for small amounts of metallic oxides which may be added in some cases to impart desired colors to the glass.

Inthe drawings:

Figs. 1 to 4, inclusive, are triaxial diagrams showing the operative limits of glass compositions having mol ratios of potassium oxide to total alkali metal oxide of 1, 0.75, 0.50, and 0, respectively, according to the present invention. Fig. la is an enlarged view of the area A1 of Fig. 1.

Fig. 5 is a light transmission curve of a glass according to the present invention in the wave length range of 0.5 to 6 microns.

Glass compositions according to the present invention are transparent amorphous compositions consisting essentially of antimony oxides, alumina, and at least one` alkali metal oxide chosen from the group consisting of sodium oxide and potassium oxide. The exact limits of suitable compositions according to the present invention are some# what irregular. In all of these compositions, the amount of antimony oxides lie within the range o'f about 25 to about 55 mol percent of the total composition. The antimony oxides are antimony trioxide and/or higher oxides of antimony. Alumina constitutes from about 13 t about 30 mol percent of the total. p The remainder consists of sodium oxide, potassium oxide,` or preferably a 2 mixture of the two. The total alkali metal oxide contentI is'from about 27 to about 45 mol percent of the total composition, and is greater than the alumina content on the mol percentage basis. 0n the basis of weight percentage, this corresponds to about 52 to about 80 percent by weight of antimony oxides reported :as the equivalent` weight of antimony trioxide, about 7 to about 22 percent-l by weight of alumina, and about l2 to about 26 percent by weight of alkali metal oxide.

Compositions lying outside the operative range according to the present invention lack sufficient transparency to be suitable for transmission of infrared radiation, and in many cases are entirely opaque. Some of these compositions are heterogeneous mixtures of transparent glass and crystalline material. Other compositions, particularly those having alumina contents slightly higher than the range according to this invention, are opaque although entirely vitreous. These compositions `in general lie close to the border o'f operative compositions according to this invention. Still other compositions of antimony oxides, alumina, and sodium and potassium oxides in proportions greatly different from the proportions according to this invention, are entirely or largely crystalline.

The operative range of glass compositions according to this invention is shown in Figs. 1 to 4, inclusive. These figures are triaxial diagrams showing the range in contents of alkali metal oxides, alumina, and antimony oxides in glasses having various ratios of potassium oxide to total alkali metal oxides. In each diagram the apices represent percent of alkali metal oxides, alumina, and antimony oxides, respectively, and the sides show mol percentages of these constituents. The designation R20 is used to `refer to the total alkali metal oxide content,- which is the combined amount of Na20 and K2O. Alumina is designated as A1203. The entire content of antimony oxides is designated as Sb203, although it is to be understood that this includes either antimony trioxide, higher o'xides of antimony, or both.

Fig. 1 shows the operative composition range in glasses having K20 as the only alkali metal oxide, and the apices are designated K20, A1203, and Sb203, respectively. Figs. 2 and 3 show the range when the mol ratio of K2O to Na2O+K2O(R20) is 0.75 and 0.50, respectively. Fig. 4 shows the operative ranges in glasses containing Na20 as the only alkali metal oxide, and the apices are designated respectively as Na20, A1203, and Sb203. In each of these figures the curved line denotes the limits o'f transparent glass compositions. For proportions of K20 to Na20, not shown in the drawings, the limits of trans` parent glass compositions can be estimated from the drawings by interpolation.

Comparison of Figs. 1 through 4 shows that the oper; ative range of antimony oxides is broadest in glasses in` which the mol ratio of K20 to total alkali metal oxides (R20) is 0.75. The range is very limited in glasses containing no Na20 (Fig. l), broadens to a maximum as the ratio of K20 to K20-I-Na20 drops to 0.75 (Fig. 2) and thereafter drops gradually (Figs. 3 and 4) as the mol ratio of K2O to total alkali metal oxides drops to zero.

Fig. 2 shows that the antimony oxide content in glasses containing 3 mols of K20 per mol of Na20` (K20/R20=0.75) may be varied from 25 to 55 mol per" cent. This corresponds to 52 to 80 percent by weight, and represents a greater range than is permissible in glasses having any other proportions ofI Na20 and K2O according to this invention. The composition range of glasses containing 3 mols of K20 per mol of Na20 is denoted by the area A2 enclosed within the curved line in Fig. 2. 27 to 45 mol percent. Alumina constitutes the balance" and amounts to 13 to 30 mol percent `of the composi-` Patented Dec. 22, 1959.,

The total alkali metal oxide content is from 3 tion. The combined mol percentage of alkali oxides always exceeds the mol percentage of alumina. The maximum amounts of alkali oxides and alumina, and the minimum amount of antimony oxides are present in a glass containing 25 mol percent antimony oxides, 45 mol percent alkali metal oxides (about 11.2 mol percent Na2O and 33.8 mol percent K2O) and 30 mol percent alumina. This composition is denoted by point B2 in Fig. 2. The minimum amount of alkali metal oxides is 27 mol percent in a glass also containing about 20 mol percent alumina and 53 mol percent antimony oxides. This composition is denoted by point E2. The minimum amount of alumina, 13 mol percent, occurs in a glass also containing about 34 mol percent of alkali metal oxides and 53 mol percent of antimony oxides. The composition is denoted by point D2. In a glass containing 40 mol percent antimony oxides, the alkali metal oxide content may vary from about 34 to 41 mol percent, and the balance is essentially alumina. These compositions are denoted by points F2 and C2, respectively.

As the mol ratio of K2O to Na2O` decreases below 3 to 1, the breadth of range of antimony oxide contents also decreases. The area A3 within the curved line of Fig. 3 represents the range of composition in glasses according to the present invention which contain equimolar amounts of Na2O and K2O.

The amount of antimony oxides is in the range of about 30 to 50 mol percent when equimolar 'amounts of Na20 to K2O are present, as shown in Fig. 3. These amounts are denoted by points B3 and D3, respectively. Point C3 represents a composition containing approximately 41 mol percent of alkali metal oxides, 19 mol percent alumina, and 40 mol percent antimony oxide. Point E3 represents a composition containing approximately 34 mol percent alkali metal oxides, 26 mol percent alumina, and 40 mol percent antimony oxide. The range of antimony oxide contents narrows considerably with further decreases in the ratio K2O to Na2O. When sodium oxide is the only metal oxide present, the antimony oxide content should lie in the range of about 36 to 46 mol percent, as shown in Fig. 4. The area A2 within the curved line of Fig. 4 represents the operative range of glass compositions according to this invention consisting of Na2O, A1203, and antimony oxides, with no K2O. Points B4 and D4 denote glasses containing the minimum and maximum antimony oxide contents, respectively. Point C4 represents a composition of about 41 mol percent Na2O, 19 mol percent alumina, and 40 mol percent antimony oxide. Point E., represents a composition of 34 mol percent Na2O, 26 mol percent alumina, and 40 mol percent antimony oxide.

The median antimony oxide content is about 40 mol percent, regardless of the relative amounts of Na2O and K2O in the glass. The permissible range in alkali metal oxide and alumina contents in glasses containing 40 mol percent antimony oxides, is virtually constant at 34 to 41 mol percent alkali metal oxides, balance alumina, at any ratio of K2O to total alkali metal oxides up to a mol fraction of 0.75.

Increases in the molar ratio of K2O to Na2O above 3 to l greatly reduce the range of operative amounts of the various ingredients. Fig. l shows that the only suitable glasses containing no Na2O are compositions of about 40 mol percent K2O, 20 mol percent A1203, and 40 mol percent antimony oxides. These compositions lie Within the very small area A1 enclosed by the curved line of Fig. l. Even these compositions are more difficult to melt into a transparent glass than most compositions according to this invention which contain some Nago.

Glasses containing from 1 to 3 mols of potassium oxide per mole of sodium oxide are preferred. Compositions lying within this range are more workable than compositions lying outside this range, and are easily formed entirely free of any crystalline or other apaque matter which reduces the transparency of glass. As the amount of potassium oxide is decreased below 50 mol percent or increased above 75 mol percent of the total alkali metal oxide content, formation of glass without inclusion of any opaque material becomes increasingly more diicult. Glasses containing about 3 mols of K2O per mol of Na2O are the best from the standpoint of workability and high transparency. Furthermore, the range of glass compositions is broader at this ratio than at any other ratio of K2O to Na2O.

Minor amounts of heavy metal oxides, rarely exceeding l percent by weight and frequently much less, about 0.05 to 0.1 percent by weight for example, may be added to the glass according to the present invention to improve the color. Generally these additions impart a color to the glass without affecting the desirable infrared transmission characteristics. In the absence of any coloring oxides, glasses according tothis invention are usually transparent and light yellow in color. A possible explanation of this yellow color is the fact that transmission of the longer rays in the visible spectrum exceeds transmission of shorter visible light rays. To lmpart desired color and to reduce transmission of visible light various coloring oxides, as for example manganese dioxide and nickelous oxide, can be used.

Ingredients which adversely aiect the infrared transmission properties of glass according to the present invention areexcluded. Silica and boron trioxide shorten the range of infrared transmission and are not present in amounts exceeding 5 percent by weight for this reason. Preferably they are entirely absent. Lithium compounds are excluded as glass containing lithium is in-4 erior in melting properties and transparency to glass containing no alkali metals except sodium and potassium. preferably glasses of the present invention contain no ingredients except antimony trioxide and possibly higher`| oxides of antimony, alumina, potassium oxide, sodium oxide, and a small quantity of color-imparting oxide if desired.

Glasses according to the present invention can be made readily by fusing antimony trioxide and alumina with salts of potassium and sodium which decompose at melting temperature leaving no residue except potassium oxide and sodium oxide, respectively. Nitrates and carbonates are examples of such salts. It is advantageous to use potassium nitrate as the source of K2O, since it is desirable to melt the batch in a mildly oxidizing atmosphere. Sodium carbonate is a suitable source of sodium in glasses containing high ratios of K2O to Na2O. Sodium nitrate is preferable as a source of at least part of the sodium in glasses containing no potassium oxide or a low ratio of potassium oxide to sodium oxide. Carbon dioxide and oxides of nitrogen are volatilized during melting, leaving a melt consisting essentially of antimony oxide, alumina, sodium oxide, and potassium oxide. Whether the antimony oxide is entirely Sb2O3 or partially higher oxides of antimony is not certain as previously stated, but it is probable that some oxidation of Sb203 takes place. Small amounts of color-imparting oxides, such as manganese dioxide, cobaltous-cobaltic oxide (C0304), and nickel oxide (NiO) are included in the batch where these ingredients are desired in the glass. A dry batch weighing 100 pounds yields a melt weighing on the average about pounds.

Other reagents which furnish the oxides of sodium, potassium, aluminum and antimony may be substituted for the foregoing. For instance, all or part of the antimony may be supplied as a pentavalent compound, such as antimony pentoxide. Sodium aluminate can be used as a replacement for sodium oxide and alumina, and sodium or potassium antimonite may be substituted for sodium or potassium oxide and antimony trioxide. Other replacements of this type will be evident.

Batches are melted by heating to a temperature of about2400 to ,265( E, flhemelting temperatures vary 2,91s,sse

within approximately this range, depending on the composition and particularly on the antimony oxide content.l

furnace in the pressure of air or in a gas-fired furnace,

with an oxidizing flame. Use of an oxidizing salt such as potassium nitrate also helps in maintaining an oxidizing atmosphere.

The melting furnace atmosphere should be dry as well as oxidizing to obtain the best transmission characteristics in the glass produced. Glass melted in a substantailly bone-dry atmosphere has a high and virtually constant infrared transmission of wave lengths up to about 6 microns. Quantities of moisture even as small as those amounts normally present in air at room temperature result in a glass which transmits virtually no rays of 3 microns in wave length and has a narrow band on either side in which transmission s substantially impaired. Transmission of rays of other wave lengths outside this band is unaffected by the presence or absence of moisture. A dry atmosphere is most easily obtained in an electric furnace equipped with a drier for the air drawn into the furnace chamber.

The molten glass is rapidly cooled after pouring to a temperature below 1000 F., and is also annealed in a preferred mode of operation. Rapid cooling can be effected by pouring the melt into a mold which has been preheated to a temperature of about 100 to about 1000 F The glass is cooled until it solidies. It is desirable to preheat the mold to some extent to avoid wrinkling of the glass adjacent the mold surface as it solidies. i

It is desirable to anneal glass of the present invention to relieve internal stresses. `This can be done by placing the solidified glass in an annealing oven maintained at a temperature of 1000 F. or lower, down to about 800 F. The length of time of annealing is not critical, and may be from a minimum of about 2 hours up to much longer times, say at least 24 hours. For example, glasses according to this invention have been satisfactorily annealed in a furnace which was initially ata temperature of about 800 to 1000" F. and gradually cooled over an interval of about 12 to 24 hours to room temperature or slightly higher, about 100 to 125 F.

Glass prepared according to the present invention is transparent to both visible and infrared light and has a yellow tinge. As has been explained, various colorimparting oxides can be present. The glass transmits approximately 55 to 75 percent of the light having wave lengths of 0.5 to 0.7 micron and slightly lower percentages of rays near the violet end of the visible spectrum (0.4 to 0.5 micron). The glass transmits infrared rays having wave lengths up to about 6 microns, and the transmission is relatively high over most of this range. For example, from about 0.7 micron up to about 5 microns, the transmission is very nearly constant at about 65 to 75 percent. The transmission falls gradually at Wave lengths from about 5 microns up to about 6 microns, except for diminished transmission at around 3 microns in some cases as previously explained. Glass which has been melted in a dry atmosphere shows substantially the same transmission at 3 microns as at other wave lengths, or at most only slightly lower transmission. Fig. 5 shows the transmission characteristics of a glass melted in a dry atmosphere according to the present invention. This glass has about 53 percent transmission at 3 microns and peak transmission of about 68 percent at 2 to 2.5 microns and again at around 4 microns. Glass which has been melted in a moist atmosphere absorbs virtually all radiation of about 3 microns in wave length.

The refractive index of glass according to the present invention is about 1.69 to about 1.76. Generally the` refractive index increases with increasing amounts of Sb203.

Glass according to the present invention is useful in virtually all devices where glass which transmits infrared radiation is required, as for example in pyrometers, bolometers, etc.

To illustrate the present invention further, the following illustrations by way of specific examples are given:

Example I A batch consisting of 6.2 grams of sodium carbonate, 35.6 grams of potassium nitrate, 15.0 grams of alumina, and 65.0 grams of antimony trioxide was mixed, placed in a Crucible and introduced into a gas-tired furnace. This batch was calculated to yield a melt of grams having a composition as follows:

Oxide Weight Mol Percent Percent The batch was heated to 2500 F. for about 30 minutes.

The melt was then poured from the crucible onto an' Example Il A 20-gram batch of a glass of the composition described in Example I was melted in a glazed porcelain boat in an electrically heated furnace. The furnace was heated to 2500 F., then the boat containing the batch was slowly pushed into the hot zone of the furnace. Air which had been previously dried was then passed into one end of the furnace. The batch was melted in about 15 minutes. The melt was withdrawn from the furnace and poured onto a at piece of sheet iron. A disk of transparent glass having a slight yellow color approximately inch in diameter was obtained. This was annealed for approximately 16 hours in a furnace which was initially at a temperature of 850 F. The furnace was allowed to cool to a temperature of about F. at the end of the annealing period.

The annealed sample was ground and polished on both sides and tested for infrared transmission. The results of these tests were as follows:

Wave length, microns: Percent transmission cally in Fig. 5.

2 The above infrared transmission data are shown graphi" Example lll A charge consisting of 7.7 grams of Na2CO3, 44.6 grams of KNOS, 20.0 grams of A1203, and 55.0 grams of and 69.3 grams of antimony trioxide was prepared. This charge was calculated to give a melt weighing 100 grams and having the following composition:

Sb203 was placed in a porcelain crucible and placed in i a gas-tired furnace. The batch was calculated to yield the Oxlde Plnt following amounts of oxides:

i??? r' 33 Oxide Weight M01 2 A10 12.1 20 Percent Percent 10 S1322 O33 n 69- 3 40 4.5 10.8 20.5 32.4 The charge was placed 1n a gas-red furnace. The ggg gz melt was heated over a period of about 30 minutes, and became very fluid with active boiling at about 2500 F. The charge was melted and was observed to boil at The melt was then poured. As the glass cooled 1t broke 2450@ F The charge Ws poured and was completely into small pieces. A few crystals were observed 1n some dex/imm@ The charge was then reheated to 2550 F of the pieces, but most of the glass pieces were clear and and poured. The second melt was entirely glass with no transparent Exam le VII crystalline phase, and was mostly colorless except for p a whitish top surface. A batch consisting of 19.3 grams of sodium carbonate, 12.4 grams potassium nitrate, 12.3 grams of alumina, and Example IV 70.8 grams of antimony trioxide was prepared. The A Charge COHSISUHS 0f 3- 8 grams 0f Sodium CabOIlflle, total of the batch was 114.8 grams, and was calculated to 27-8 grams 0f Potassium Unrat?, 100 gfamspf 31111D1113, yield a melt weighing 100 grams and having the followand 75.0 grams of antlrnony trioxide was mlxed, placed 20 ing composition: 1n a crucible, and introduced lnto a gas-fired furnace. The charge was calculated to yield a melt weighing 100 grams and having the following composition: omda picflllt oxide weight M01 30 Nazo 11.2 au Percent Percent 5.7 10 12.3 20 2 2 6 7 70.8 4o 12s 259 g1g 35 A SO-gram portion of the batch was placed in a glazed Crucible, introduced into a gas-fired furnace, and melted.

The charge was placed in a porcelain crucible and introduced into a gas-tired furnace. It was melted over a period of about 30 minutes and was observed to boil rapidly at 2450 F. The batch was heated until a temperature of 2520 F. was reached, at which time the batch was still bubbling actively at the edges. The sample was then poured into an iron mold, placed in an annealing furnace which was initially at a temperature of about 900 F., and annealed for a period of about 16 hours while the furnace was gradually cooled. The furnace was at a temperature of about 100 F. to 125 F. when the annealed sample was removed. The annealed sample was a very clear glass.

Example V A charge consisting of 6.2 grams of sodium carbonate, 35.6 grams of potassium nitrate, 11.9 grams of alumina, 68.1 grams of antimony trioxide lwas prepared. This charge Was calculated to give a melt Weighing 100 grams and having the following composition:

Oxide Weight Mol Percent Percent 3. 6 10 16. 4 30 l1. 9 20 G8. l

Example VI A charge consisting of 12.7 grams of sodium carbonate, 24.3 grams of potassium nitrate, 12.1 grams of alumina,

A batch of 26.3 grams of sodium carbonate, 12.6 grams of alumina, and 72 grams of antimony trioxide was prepared. This batch was calculated to yield a melt weighing grams and having the following composition in terms of the oxides present:

Oxide Weight Mol Percent Percent NagO 15. 4 40 A 3 12. 6 20 S102 O3 72. 1 l10 The batch was placed in a crucible and charged to a furnace and melted in about 30 minutes. The melt was heated to 2350 F. and poured onto an iron sheet to form two disks on flat pieces of iron. The disks were placed in an annealing oven which was initially at a temperature 750 F., and cooled for a period of about 16 hours. At the end of this time the oven temperature was about 100 F.

The rst disk poured was a clear, amber glass except for a whitish skin on top and some opaque inclusions. The second disk was partially devitritied and contained many inclusions.

Glass prepared according to this example was observed to be water soluble to an appreciable extent. Freshly broken edges of samples of the glass etched quite rapidly and the surfaces became aked from the dissolved alkali.

Various modications in the present invention can be made by those skilled in the art without departing from the scope thereof. The present invention shall be limited in scope only by the appending claims.

What is claimed is:

1. A transparent glass composition consisting essentially of antimony oxide, alumina, and at least one material selected from the group consisting of sodium oxide land potassium oxide; in relative amounts lying within the areas A1, A2, A3, and A4 designated in Figs. 1 to 4 inclusive of the accompanying drawing.

2. A transparent glass composition consisting essentially of antimony oxide, alumina, and sodium oxide and potassium oxide in approximately the molar ratio l to 3, in relative amounts lying within the area designated A2 in Fig. 2 of the accompanying drawing.

3. A transparent glass composition consisting essentially of antimony oxide, alumina, and at least one material selected from the group consisting of sodium oxide and potassium oxide; in relative proportions lying within the range designated by the areas A1, A2, A3, and A4 as shown in Figs. 1 to 4 inclusive of the accompanying drawing and interpolations with varying R20 therebetween.

4. A process of producing an antimony oxide glass which comprises melting antimony trioxide, alumina, and at least one decomposable compound which yields an alkali metal oxide selected from the group consisting of sodium oxide and potassium oxide, in an oxidizing atmosphere in proportions such that the resulting melt consists essentially of antimony oxide, alumina, and at least one material selected from the group consisting of sodium oxide and potassium oxide, in relative proportions lying within the range designated by the areas A1, A2, A3, and A4 of Figs. 1 to 4 inclusive of the accompanying drawings, and interpolations with varying R20 therebetween.

5. A process of producing an antimony oxide glass which comprises melting antimony trioxide, alumina, a decomposable compound which yields sodium oxide, and a decomposable compound which yields potassium oxide,

10 in an oxidizing atmosphere in proportions such that the resulting melt consists essentially of antimony oxide, alumina, sodium oxide, and potassium oxide in relative proportions lying within the range designated by the area A2 of Fig. 2 of the accompanying drawings.

6. A process of producing an antimony oxide glass which comprises melting compounds yielding a melt consisting essentially of antimony oxide, alumina, and at least one alkali metal oxide selected from the group consisting of sodium oxide and potassium oxide, the proportions of reagents being such that the melt consists essentially of antimony oxide, alumina, and at least one alkali metal oxide selected from the group consisting of sodium oxide and potassium oxide, in relative proportions lying within the range designated by the areas A1, A2, A3, and A4 in Figs. 1 to 4 inclusive of the accompanying drawings and interpolations with varying R20 therebetween.

7. A transparent glass composition consisting essentially of about 25 to 55 mol percent of antimony oxide, about 13 to 30 mol percent of A1203, and about 27 to 45 mol percent R20, where R20 is chosen from the group consisting of Na20, K2O, and mixtures thereof, said glass containing not more than about 5 percent by weight of boron trioxide and silica and transmitting at least about percent of infrared rays of wave lengths of less than about 5 microns.

8. A transparent glass composition consisting essentially of about 25 to 55 mol percent of antimony oxide, abo-ut 13 to 30 mol percent of alumina, and a sum total of about 27 to 45 mol percent of sodium oxide and potassium oxide, the mol ratio of potassium oxide to sodium oxide being about 3 to 1.

References Cited in the file of this patent Eitel et al.: Glastechnische Tabellen (1932), pp. 706- 707. 

1. A TRANSPARENT GLASS COMPOSITION CONSISTING ESSENTIALLY OF ANTIMONY OXIDE, ALUMINA, AND AT LEAST ONE MATERIAL SELECTED FROM THE GROUP CONSISTING OF SODIUM OXIDE AND POTASSIUM OXIDE; IN RELATIVE AMOUNTS LYING WITHIN THE AREAS A1, A2, A3, AND A4 DESIGNATED IN FIGS. 1 TO 4 INCLUSIVE OF THE ACCOMPANYING DRAWING. 